Testing two nuclear physics approximations used in the standard leaky box model for the spallogenic production of LiBeB

Abstract

The spallative production rates of Lithium, Beryllium and Boron (LiBeB) are a necessary component in any calculation of the evolution of these nuclei in the Galaxy. Previous calculations of these rates relied on two assumptions relating to the nuclear physics aspects: the straight-ahead approximation that describes the distribution of fragment energies and the assumption that the major contributor to the production rate arises from single-step reactions between primary cosmic ray projectiles and interstellar medium targets. We examine both assumptions by using a semi-empirical description for the spall's energy distribution and by including the reactions that proceed via intermediary fragments. After relaxing the straight-ahead approximation we find the changes in the production rates and emerging fluxes are small and do not warrant rejection of this approximation. In contrast we discover that two-step reactions can alter the production rate considerably leading to noticeable increases in the efficiency of producing the LiBeB nuclei. Motivated by this result we introduce a cascade technique to compute the production rates exactly and find that the results differ only slightly from those of our two-step calculations. We thus conclude that terminating the reaction network at the two-step order is sufficiently accurate for current studies of spallation.